Avoid a string copy in URLRequestResourceBundleJob::GetData().

base/strings/string_util.cc

Index: base/strings/string_util.cc
diff --git a/base/strings/string_util.cc b/base/strings/string_util.cc
index 43f15a360d93ba908e075307b80c01004167ed2e..f77034b35c55ad1aac7c408f8362f1e54abffa93 100644
--- a/base/strings/string_util.cc
+++ b/base/strings/string_util.cc
@@ -406,7 +406,7 @@ bool IsStringASCII(const std::wstring& str) {
 }
 #endif
 
-bool IsStringUTF8(const std::string& str) {
+bool IsStringUTF8(const StringPiece& str) {
   const char *src = str.data();
   int32 src_len = static_cast<int32>(str.length());
   int32 char_index = 0;